A hollow elastic tube is expanded and contracted in a radial direction thereof by a fluid supplied to and discharged from an inside of the elastic tube, and also extended and contracted in a length direction thereof. Patent document 1 discloses an actuating apparatus provided with: an elastic tube and head pieces serving as fixing tools to be attached to two ends thereof. This elastic tube is constituted by a hose main body and strands knitted inside the hose main body, that is, twisted yarns. The head piece is composed of: an inside part that is fitted to the inside of the elastic tube and an outside part that is fitted to the outside of the elastic tube, and each end of the elastic tube is fixed between the inside part and the outside part. An annular protrusion is formed on an outer circumferential face of the inside part so as to enhance a fastening force of the elastic tube by the outside part. This actuating apparatus is applicable as an actuator that carries out an extension and contraction operation and a bending operation by expanding and contracting the elastic tube by using a fluid.
A bendable actuator is disclosed in Patent document 2. This actuator is provided with: a tube-shaped member made of rubber or a rubber-state elastic member; and an elastic extension member composed of a net-shaped reinforcing structure, that is, a knitted strand structure, which is arranged around the outside thereof. Each end of the elastic extension member is fixed between a sealing member fitted to the elastic expansion member and a caulking ring attached to the outside of the elastic extension member. This actuator carries out an extension and contraction operation and a bending operation by expanding and contracting the elastic extension member by using a fluid supplied to and discharged from the tube-shaped member. There are two types in the actuator, that is, one type constituted by one elastic extension member, and another type constituted by a plurality of elastic extension members bound together.